[PATCH 15/48] bpf: Choose RCU Tasks based on TASKS_RCU rather than PREEMPTION

[Uladzislau Rezki (Sony)]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

The advent of CONFIG_PREEMPT_AUTO, AKA lazy preemption, will mean that
even kernels built with CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY
might see the occasional preemption, and that this preemption just might
happen within a trampoline.

Therefore, update bpf_tramp_image_put() to choose call_rcu_tasks()
based on CONFIG_TASKS_RCU instead of CONFIG_PREEMPTION.

This change might enable further simplifications, but the goal of this
effort is to make the code safe, not necessarily optimal.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Yonghong Song <yonghong.song@xxxxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: <bpf@xxxxxxxxxxxxxxx>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
 kernel/bpf/trampoline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index db7599c59c78..88673a4267eb 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -333,7 +333,7 @@ static void bpf_tramp_image_put(struct bpf_tramp_image *im)
 		int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP,
 					     NULL, im->ip_epilogue);
 		WARN_ON(err);
-		if (IS_ENABLED(CONFIG_PREEMPTION))
+		if (IS_ENABLED(CONFIG_TASKS_RCU))
 			call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
 		else
 			percpu_ref_kill(&im->pcref);
-- 
2.39.2